Bug Description

WHAT HAPPENS CURRENTLY:

We currently have two easy ways to semi-maximise windows to the left and to the right of the screen by using the keyboard shortcuts "ctrl + super + left or right".

It would be great to be able to easily semi-maximise windows to the bottom and to the top of the screen, in particular for people using square monitors, and for apps that require horizontal space to be readable.

This is already possible by using "ctrl + alt + KP8 or KP2" (numbers on the keypad). However, those are not easy to discover (they are not shown in the keyboard shortcuts overlay), are not adapted to smaller keyboards without keypads, and are inconsistent with the two other keyboard shortcuts.

WHAT NEEDS TO BE DONE:

To make them more accessible, we should:
* Redefine keyboards shortcuts, as currently ctrl + super + left or right control the semi-maximisation, whereas ctrl + super + up or down controls respectively maximisation and restoring original window size. This could for example be changed to:
- ctrl + super + arrows for 4 different semi-maximisations. This could even be extended to double arrow hits in order to add the four corners "quarter-maximisation".
- ctrl + shift + up or down for respectively maximising and restoring (and minimising, as it should already be the case as stated in the keyboard shortcuts overlay). This could however interfere with the selection keyboard shortcuts - maybe "ctrl + alt gr + up or down" is a better option?
* Adding those keyboard shortcuts to the keyboard shortcuts overlay.